System for distributing pressurized gas from a liquefied gas source

ABSTRACT

Device enabling the automatic supply of a point of distribution of gas under pressure such as butane and propane from a tank supplied with liquefied gas. The device comprises a thermal pump and a vaporizer mounted in series and control means ensuring a continuous and automatic supply of said point of distribution with vaporized gas.

United States Patent lung 5] Dec. 9, 1975 [5 1 SYSTEM FOR DISTRIBUTING 3,262,280 7/1966 Chaney 62/55 3,271,966 9/1966 Webb 62/50 PRESSURIZED GAS FROM A LIQUEFIED GAS SOURCE Inventor: Jacques Iung, Pontarlier, France Assignee: Gurtner, S.A., Paris, France Filed: July 24, 1974 Appl NO; 491,505

Foreign Application Priority Data Aug 8, 1973 France 73.29034 US. Cl 62/55; 137/210 Int. Cl. F17C 7/02 Field of Search .1 62/50, 51, 55; 137/210,

References Cited UNITED STATES PATENTS Balcar et a1 1, 62/50 Primary Examiner-Carroll B. Dority, Jr. Assistant Examiner-Ronald C. Capossela Attorney, Agent, or Firm-Steinberg & Blake [57] ABSTRACT Device enabling the automatic supply of a point of distribution of gas under pressure such as butane and propane from a tank supplied with liquefied gas. The device comprises a thermal pump and a vaporizer mounted in series and control means ensuring a con tinuous and automatic supply of said point of distribution with vaporized gas.

10 Claims, 9 Drawing Figures U.S. Patent Dec. 9, 1975 Sheet 1 of5 3,925,048

US. Patent Dec. 9, 1975 Sheet 2 01-"5 3,925,048

U.S. Patent Dec. 9, 1975 Sheet 3 of 5 3,925,048

US. Patent Dec. 9, 1975 Sheet 4 of5 3,925,048

US. Patent Dec. 9, 1975 Sheet 5 of5 3,925,048

SYSTEM FOR DISTRIBUTING PRESSURIZED GAS FROM A LIQUEFIED GAS SOURCE The present invention relates essentially to improvements to the method and device for feeding under pressure a liquefied gas contained in a storage tank as disclosed in U.S. patent application Ser. No. 364,739 filed May 29, 1973 in the name of the same applicant.

According to said U.S. patent application there has been described a device enabling a point of distribution of gas under pressure to be supplied with liquid constituted by liquefied gas, such as liquefied petroleum gas comprising butane and propane from a storage tank filled at least partially with said liquid. The device comprises a first container of relatively small capacity communicating with said tank through a first duct permitting the flow of the liquid contained in the tank towards the said first container, further means being provided allowing the supplying of said first container with said liquid each time the first container has been emptied. Heating means are provided in said first container with a view to form a thermal pump, the liquid contained in said container being allowed to be expelled under pressure into a second container each time the pressure in said first container is sufficient due to the supplying of heat by said heating means in said first container. In said device the second container constitutes a vaporizer in which the liquefied gas is vaporized with a view to supply the distribution point with the necessary gas.

According to the present invention a device is disclosed which allows the automatic distribution of gas under pressure for a point of distribution from a device comprising a storage tank, a thermal pump and a vaporizer of the type described.

According to the invention a first duct on which is mounted a first valve connects the tank to said first container permitting the flow of the liquid contained in the tank towards the said first container each time the liquid level in said first container lowers below a minimal predetermined level.

Furthermore a second duct on which is mounted a second valve connects said first container to said second container permitting the flow of the liquid contained in said first container towards said second container each time the liquid level in said second container lowers below a predetermined minimal level.

The valves are automatically controlled by signals supplied by detection means provided in each container detecting said liquid level.

The invention will be better understood and further objects, characterizing features, details and advantages thereof will appear more clearly as the following explanatory description proceeds with reference to the accompanying diagrammatic drawings given by way of non-limiting example only illustrating a presently preferred embodiment of the invention and wherein:

FIG. 1 is a diagrammatic view showing the general lay-out or arrangement of the liquefied petroleum gas distribution plant including the improvements forming the subject matter of the present invention;

FIG. 2 is a top view of an improved thermal pump according to the present invention;

FIG. 3 is an axial sectional view taken upon the line III-III in FIG. 2;

FIG. 4 is a vertical section taken substantially upon the line IVIV in FIG. 2 with parts broken away;

FIG. 5 is a section through a detail, taken upon the line VV in FIG. 2 and drawn on a larger scale;

FIG. 6 shows on a larger scale the detail designated by the arrow VI in FIG. 3;

FIG. 7 is a top view of an improved vaporizer according to the invention;

FIG. 8 is a view in vertical section taken upon the line VIll-VIII in FIG. 7; and

FIG. 9 is a view in vertical section taken upon the line lX-IX in FIG. 7.

According to the embodiment shown the storage tank or cistern forming a supply tank means containing the liquefied gas including its liquid phase 113 and its gaseous phase 112 feeds a distribution duct means or utilization point 115 by means of an intermediate container means 117 forming a heat pump and of a vaporizer 114 as disclosed in said U.S. patent application Ser. No. 364,739.

According to the present invention, in the heat pump 117 and an output container means in the form vaporizer 114 are used like control means, unidirectional sys terns 116, 118 for controlling their filling and emptying cycle. As clearly seen in the diagram of FIG. 1 such a undirectional system comprises in particular a float 119, 120 located within the containers of the heat pump 117 and vaporizer 114, respectively, with a view to detect or sense the level of liquid, a mechanism 121, 122 forming a quick opening over-center or snapswitch means operated or driven in either direction when the float moves through or past a predetermined level and an electro-magnetic or solenoid-operated valve means 123, 124 controlled for being opened by said snap-switch means when the float moves downwards past and below said level and for being closed when the float moves upwards past and above said level. The mechanism forming a quick opening snapswitch 121, 122 comprises a magnetic contact piece 125, 126 urged against the inner walls of the heat pump and vaporizer, respectively, when the float 119, 120 is located underneath said level. Inside of the heat pump 117 and vaporizer 114 are arranged magnetic switches 185, 186 mounted in the circuits for energizing the electro-magnetic valves 123, 124, respectively. The heating means or device 127 for partially heating and vaporizing the liquid phase 128 within the heat pump 117 is electrically mounted in parallel with the energizing circuit of the electro-magnetic valve 123. The electric heating-device 127 of the vaporizer is however used in principle at the start of the plant only as described in said U.S. patent application Ser. No. 364,739 the vaporization being provided during the normal working cycle by a heating means in the form of a hot-water circulation 198 (FIGS. 8 and 9).

The heat pump 1 17 is supplied with liquified gas from the tank 1 10 through the feed duct means 129 and the closing valve means 130 of the electro-magnetic valve 123.

The heat pump 117 and the vaporizer 114 are connected by the supply duct means 131. In the manner described in said U.S. patent application the heat pump 117 discharges liquid (liquefied gas) through the check or safety valve means 132 into the duct 131 which conveys the liquid towards the vaporizer 114. The flow of this liquid into the vaporizer 114 through the closure valve means 133 of the electro-magnetic valve 124 is controlled by the unidirectional system 118 of the vaporizer in a manner like that described hereinabove for the unidirectional system 116 of the pump.

The improved arrangement illustrated in FIG. I also comprises safety means. Thus in FIG. 1 is shown a 3 safety valve means 134 which enables the escape of the gaseous phase contained in the heat pump 117 through the duct 188 into the tank 110 in case of overpressure. The tank 110 is fitted with a regular safety valve 184.

According to the present invention the check valve 132 is designed as described in more detail hereinafter as a valve which also enables the flow of liquid in the direction from the feed duct 131 to the heat pump 117 when an overpressure exceeding a certain valve occurs in said duct.

In the vaporizer there has also been provided for the possibility of allowing the gas to escape through the duct 131 towards the heat pump 117 when an overpressure occurs in the vaporizer as will be described below with reference to FIG. 9.

The improvements forming the subject matter of the invention will now be described in detail more particularly with reference to FIGS. 3 to 9.

As seen in FIGS. 3 and 4 the liquefied gas is fed through the supply duct 129 from the tank 110 into the enclosed space 136 of the heat pump 117.

The container 136 contains a float 119 and the mechanism forming a quick opening snap-switch 121 carrying the magnetic piece 125. The mechanism 121 consists essentially of a bent or bell-crank lever 137 mounted for rotation or swinging motion about a shaft 138 and connected to the lower portion of the float 119, a second lever 139 also mounted for rotation about a stationary shaft 140 and secured to a resilient element such as a spring 141 with one end connected to the lever 139 at a location 139a remote from the axis of rotation 140 and with the other end connected at 142a to a third arm 142 forming part of the lever 137 and extending from the bend of the latter. The arm 142 and the lever 139 are therefore both adapted to swing or rotate about the stationary shafts 138, 140, respectively, approximately in approximately opposite directions. The free end of the lever 139 extends into a recess 143 formed in the wall of the enclosed space 136 and carries the piece 125 which controls the magnetic switch 185 illustrated in FIG. 1 and adapted to connect or not the solenoid coil or winding of the electro-magnetic valve 123 to the ac. voltage source or supply 194.

In FIG. 4 is seen the construction of the electro-magnetic valve 123. It essentially comprises the coil 144 which operates the closure means 130 (FIG. 1) consisting of the valve member 145 carrying a seal or like fluid-tight packing 147 on its face facing its seat 146. The valve member 145 is mounted on the rod 148 which extends substantially in coaxial relation to the coil into the central bore of which it extends more or less deeply against the action of the spring 149 according as an electric current for energizing the electromagnetic valve is or not flowing through the coil.

The energizing of the electro-magnetic valve and its operation for opening towards the container 136 by lowering of the valve member 145 depend upon the position of the magnetic piece 125 within the recess 143. It is the position of the float 119 which compulsorily follows any fluctuation of the level of liquid within the enclosed space 136 which determines the position of the magnetic piece 125. According as the float is located below or above a certain level within the container 136, the arm 142 of the lever is located to the left or to the right of a line passing through both axes of rotation 140 and 138. Owing to the provision of the spring 141, it causes the lever 139 to rock or tilt from one side to the other every time it passes through this line. The magnetic piece is accordingly urged or applied either against the left-hand wall or against the right-hand wall of the recess 143. At 187 is mounted a counterweight for the float 119. In FIGS. 8 and 9 is seen the unidirectional system 118 associated with the vaporizer 114 for controlling its filling and its emptying. The portion located inside of the enclosed space 150 of the vaporizer 114 is very similar to that used in the heat pump and will therefore not be described again. The elements already described are designated by the same reference numerals as those which have already been described in detail hereinabove. These FIGS. however show the position assumed inside of the enclosed space 150 by the magnetic switch 186 mounted in the loop or circuit for energizing the electro-magnetic valve 124.

The electro-magnetic valve 124 used in the vaporizer 114 has the only particular feature with respect to the electro-magnetic valve 123 that its closure means 133 are mounted in the duct 153 connecting the enclosed space 150 of the vaporizer to the feed duct 131 leading at 151 into the vaporizer casing connecting the vaporizer and the heat pump so that the valve member 154 also allows the passage of gas in the direction from the vaporizer to the heat pump when an overpressure occurs within the enclosed space 150 of the vaporizer 1 14.

As more clearly shown in FIG. 9, the fluid passes from the duct 131 into the enclosed space 150 of the vaporizer while flowing through the various portions designated at 151, 155, 153' and 153 of a duct supplying fluid to the vaporizer. The portion 153 is enlarged and forms a cylindrical bore 155 with a larger diameter the centre axis of which is sloping downwards. Within this bore 155 is positioned a filter means 156 adapted to prevent any particle of solid matter from entering the container 150. The bore 155 is extended to the outer face of the vaporizer casing. A spring means 157 is inserted therein and the filter 156 bears upon the end of said spring. The filter-spring assembly is kept in position by a threaded plug 158 accessible from the outside. Since the centre axis of the filter 156 and spring 157 coincide, the filter may be pushed back against the action of the spring and thereby free or disengage the duct 153 when an overpressure occurs within the portion of the duct 153 communicating with the container 150 or within the latter itself and when the filter is clogged.

FIG. 5 and 6 show other safety means also provided to avoid endangering the plant by overpressures occurring within the heat pump 117 and within the feed duct 131 through which the heat pump and the vaporizer 114 communicate with each other.

In FIG. 5 is shown in more detail the ball check valve 134 allowing the escape of the gaseous phase from the heat pump 117 towards the tank in case of overpressure within the pump. The valve 134 is mounted within a bore provided in the wall of the pump casing near the electro-magnetic valve 123. As known per se this valve comprises a ball 135 mounted in opposing relation to a spring 136 kept in position by a screw-threaded plug 137. On the occurrence of an overpressure the ball is pushed back and thus disengages or frees the passageway 187 communicating with the escape or eduction duct 188 (FIGS. 1 and 2) connecting the pump to the tank.

FIG. 6 shows a check valve provided with a release valve 132 which connects the enclosed space of the heat pump to the feed duct 131 opening through the closure means 133 into the vaporizer 114. This check valve provided with safety valve, mounted within a bore of the vaporizer casing 117 essentially comprises a ball valve of a known type such as the valve 134 shown in FIG. 5 and the seat of which is provided in a piston or plunger 159 slidably mounted within a bore 170 provided in the wall of the pump 117 in opposite relation to the reaction of a resilient element such as a spring 160 bearing onto the stationary portion 161 of the valve body or casing in which the piston slides. The piston or plunger 159 consists of two cylindrical parts 162, 163. The member 162 accommodates the ball 164 and serves as the seat proper for the latter whereas the member 163 provides for keeping the ball l64-spring 165 assembly in position. F or this purpose the member 162 is set or fitted into the member 163. The heat pump 117 and said feed duct 131 communicate through the passageway 166 machined in both members 162 and 163. Thus the liquid from the pump 117 may enter the duct 131 while pushing the ball 164 back in the direction of this duct against the reaction of the spring 165. I

The piston 163 comprises on its face directed towards the duct 131 a seal or fluid-tight packing member 167 which under the action of the resilient element 160 is caused to bear against a seat 168 formed in a connecting member 169 screwed into the portion of the pump 117. In the circumferential face of the member 163 are machined grooves 171. Under normal operating conditions, no liquid may flow from the feed duct 131 towards the pump 117 as the passageway 166 which extends through the piston 162 is closed by the ball 164 and the seal 167 provides for a fluid-tight bearing of the member 163 onto the seat 168.

When however an overpressure occurs within the vaporizer 114 or within the feed duct 131 the piston is pushed back against the opposing spring 160. This is effective for disengaging or moving the sealing member 167 of the piston 163 away from its seat 168 and enabling the flow of liquid through the grooves 171 provided between the circumferential face of the piston and the bore 170, from the vaporizer 114 or from the duct 131 towards the pump 117.

The check valve provided with a safety valve may for instance be calibrated or set in such a manner that the flow from the pump towards the duct 131 occurs for an overpressure in this direction exceeding 1 bar whereas the flow in the direction from the duct 131 to the heat pump will be possible when the overpressure in this direction exceeds the value of 2 bars. Moreover the valve 134 will prevent any overpressure within the plant due to automatic escape towards the tank 110 provided with a safety valve 184 for venting to the atmosphere.

It should be understood that the invention is not at all limited to the form of embodiment described and shown which has been given by way of example only. It indeed covers all the means forming technical equivalents of the means described as well as their combinations if same are carried out according to the gist of the invention and used within the scope of the appended claims.

What is claimed is:

l. [n a system for distributing pressurized gas from a liquefied gas source, supply tank means for containing the gas which is to be distributed in an upper gaseous phase and a lower liquid phase, output container means smaller than said storage tank means for also containing the gas which is to be distributed in an upper gaseous phase and a lower liquid phase, distributing duct means communicating with said output container means at said upper gaseous phase thereof for receiving from said output container means the gas which is to be distributed, intermediate container means smaller than said supply tank means for also containing the gas which is to be distributed in an upper gaseous phase and a lower liquid phase situated in said intermediate container means, supply duct means communicating with a lower portion of said supply tank means and an upper portion of said intermediate container means for supplying liquefied gas from said supply tank means to said intermediate container means, electromagnetic valve means operatively connected with said supply duct means for opening and closing the same to control the supply of liquefied gas from said supply tank means to said intermediate container means, connecting duct means connecting a lower portion of said intennediate container means with an upper portion of said output container means for supplying liquefied gas from said intermediate container means to said output container means, electromagnetic valve means operatively connected with said connecting duct means for controlling the flow of liquefied gas from said intermediate container means to said output container means, a pair of control means respectively situated in said intermediate and output container means and respectively cooperating with the pair of electromagnetic valve means operatively connected with said supply duct means and connecting duct means for respectively opening said valves when the liquid level of the liquid phase reaches a given lower elevation and closing said valves when said liquid level reaches a given upper elevation, a pair of heating means respectively situated in said intermediate and output container means for heating the interiors thereof, and means controlling the heating means of said intermediate container means when said electromagnetic valve means operatively connected with said supply duct means is closed.

2. The combination of claim 1 and wherein said connecting duct means also has operatively connected therewith a valve means for normally permitting flow only in a direction from said intermediate container means toward said output container means.

3. The combination of claim 1 and wherein a safety duct means communicates with an upper portion of said intermediate container means and an upper portion of said supply tank means and carries a safety valve means for providing for flow of gas from said intermediate container means toward said supply tank means when an excessive pressure is present in said intermediate container means.

4. The combination of claim 1 and wherein said connecting duct means carries a safety valve means for providing for flow from said output container means toward said intermediate container means when an excessive pressure exists in said output container means.

5. The combination of claim 4 and wherein said safety valve means is situated at a region of said connecting duct means which is adjacent said intermediate container means.

6. The combination of claim 4 and wherein said electromagnetic valve means operatively connected with said connecting duct means responds to excessive pressure in said output container means for automatically opening when said excessive pressure is present.

7. The combination of claim 1 and wherein each of said control means includes a float and an over-center means operated thereby, said over-center means in said intennediate container means controlling said electromagnetic valve means which is operatively connected with said supply duct means while said over-center means in said output container means controls said electromagnetic valve means which is operatively connected with said connecting duct means.

8. The combination of claim 7 and wherein each of said over-center means includes a magnetic element moved between a pair of positions for controlling the electromagnetic valve means.

9. The combination of claim 1 and wherein said connecting duct means has a filter means in its interior as well as a spring means acting on said filter means for yieldably maintaining the latter in a position from which said filter means is adapted to yield in opposition to said spring means when an excessive pressure is present in said output container means.

10. The combination of claim 1 and wherein said connecting duct means carries, for normally preventing reverse flow from said output container means back to said intermediate container means, a valve seat in said connecting duct means, a piston normally engaging said valve seat and a spring urging said piston into engagement with said valve seat, said spring urging said piston in the direction of flow from said intermediate container means to said output container means against said valve seat, and said piston being formed with a bore passing therethro ugh and containing a check valve means for permitting flow through said bore of said piston only from said intermediate container means toward said output container means, said piston having an exterior surface formed with axial grooves so that when an excess of pressure occurs in said output container means the excess of pressure will act on said piston to displace the latter away from said seat permitting flow through said grooves at the exterior of said piston back toward said intermediate container means. =1 

1. IN A SYSTEM FOR DISTRIBUTING PRESSURIZED GAS FROM A LIQUEFIED GAS SOURCE, SUPPLY TANK MEANS FOR CONTAINING THE GAS WHICH IS TO BE DISTRIBUTED IN AN UPPER GASEOUS PHASE AND A LOWER LIQUID PHASE, OUTPUT CONTAINER MEANS SMALLER THAN SAID STORAGE TANK MEANS FOR ALSO CONTAINING THE GAS WHICH IS TO BE DISTRIBUTED IN AN UPPER GASEOUS PHASE AND A LOWER LIQUID PHASE, DISTRIBUTING DUCT MEANS COMMUNICATING WITH SAID OUTPUT CONTAINER MEANS AT SAID UPPER GASEOUS PHASE THEREOF FOR RECEIVING FROM SAID OUTPUT CONTAINER MEANS THE GAS WHICH IS TO BE DISTRIBUTED, INTERMEIDATE CONTAINER MEANS SMALLER THAN SAID SUPPLY TANK MEANS FOR ALSO CONTAINING THE GAS WHICH IS TO BE DISTRIBUTED IN AN UPPER GASEOUS PHASE AND A LOWER LIQUID PHASE SITUTATED IN SAID INTERMEDIATE CONTAINER MEANS, SUPPLY DUCT MEANS COMMUNICATING WITH A LOWER PORTION OF SAID SUPPLY TANK MEANS ZND AN UPPER PORTION OF SAID INTERMEIDATE CONTAINER MEANS FOR SUPPLYING LIQUEFIED GAS FROM SAID SUPPLY TANK MEANS TO SAID INTERMEDIATE CONTAINER MEANS, ELECTROMAGNETIC VALVE MEANS OPERATIVELY CONNECTED WITH SAID SUPPLY DUCT MEANS FOR OPENING SAID CLOSING THE SAME TO CONTROL THE SUPPLY OF LIQUEFIED GAS FROM SAID SUPPLY TANK MEANS TO SAID INTERMEDIATE CONTAINER MEANS, CONNNECTING DUCT MEANS CONNECTING A LOWER PORTION OF SAID INTERMEDIATE CONTAINER MEANS WITH AN UPPER PORTION OF SAID OPUT CONAINER MEANS FOR SUPPLYING LIQUEFIED GAS FROM SAID INTERMEDIATE CONTAINER MEANS TO SAID OUTPUT CONTAINER MEANS ELECTROMAGNETIC VALVE MEANS OPERATIVELY CONNECTED WITH SAID CONNECTING DUCT MEANS FOR CONTROLLING THE FLOW OF LIQUEFIED GAS FROM SAID INTERMEDIATE CONTAINER MEANS TO SAID OUTPUT CONTAINER MEANS, A PAIR OF CONTROL MEANS REPECTIVELY SITUATED IN SAID INTERMEDIATE AND OUTPUT CONTAINER MEANS AND RESPECTIVELY COOPERATING WITH THE PAIR OF ELECTROMAGNETIC VALVE MEANS OPERATIVELY CONNECTED WITH SAID SUPPLY DUCT MEANS AND CONNECTING DUCT MEANS FOR RESPECTIVELY OPENING SAID VALVES WHEN THE LIQUID LEVEL OF THE LIQUID PHASE REACHES A GIVEN LOWER ELEVATION AND CLOSING SAID VALVES WHEN SAID LIQUID LEVEL REACHES A GIVEN UPPER ELEVVATION, A PAIR OF SAID LIQUID LEVEL REACHES A GIVEN UPPER ELEVATION, A PAIR OF OUTPUT CONTAINER MEANS FOR HEATING THE INTERIORS THEREOF, AND MEANS CONTROLLING THE HEATING MEANS OF SAID INTERMEDIATE CONTAINER MEANS WHEN SAID ELECTROMAGNETIC VALVE MEANS OPERATIVELY CONNNECTED WITH SAID SUPPLY DUCT MEANS IS CLOSED.
 2. The combination of claim 1 and wherein said connecting duct means also has operatively connected therewith a valve means for normally permitting flow only in a direction from said intermediate container means toward said output container means.
 3. The combination of claim 1 and wherein a safety duct means communicates with an upper portion of said intermediate container means and an upper portion of said supply tank means and carries a safety valve means for providing for flow of gas from said intermediate container means toward said supply tank means when an excessive pressure is present in said intermediate container means.
 4. The combination of claim 1 and wherein said connecting duct means carries a safety valve means for providing for flow from said output container means toward said intermediate container means when an excessive pressure exists in said output container means.
 5. The combination of claim 4 and wherein said safety valve means is situated at a region of said connecting duct means which is adjacent said intermediate container means.
 6. The combination of claim 4 and wherein said electromagnetic valve means operatively connected with said connecting duct means responds to excessive pressure in said output container means for automatically opening when said excessive pressure is present.
 7. The combination of claim 1 and wherein each of said control means includes a float and an over-center means operated thereby, said over-center means in said intermediate container means controlling said electromagnetic valve means which is operatively connected with said supply duct means while said over-center means in said output container means controls said electromagnetic valve means which is operatively connected with said connecting duct means.
 8. The combination of claim 7 and wherein each of said over-center means includes a magnetic element moved between a pair of positions for controlling the electromagnetic valve means.
 9. The combination of claim 1 and wherein said connecting duct means has a filter means in its interior as well as a spring means acting on said filter means for yieldably maintaining the latter in a position from which said filter means is adapted to yield in opposition to said spring means when an excessive pressure is present in said output container means.
 10. The combination of claim 1 and wherein said connecting duct means carries, for normally preventing reverse flow from said output container means back to said intermediate container means, a valve seat in said connecting duct means, a piston normally engaging said valve seat and a spring urging said piston into engagement with said valve seat, said spring urging said piston in the direction of flow from said intermediate container means to said output container means against said valve seat, and said piston being formed with a bore passing therethrough and containing a check valve means for permitting flow through said bore of said piston only from said intermediate container means toward said output container means, said piston having an exterior surface formed with axial grooves so that when an excess of pressure occurs in said output container means the excess of pressure will act on said piston to displace the latter away from said seat permitting flow through said grooves at the exterior of said piston back toward said intermediate container means. 